Instructions
Preparation
Make sure you have played his story mode through at least once.
Buff his skills up as much as possible, making sure you've powered him up all the way.
Reset him to level 1. We recommend powering him up first, but if you try with a fully powered Goemon and fail, try this.
Equip him with the War Rations (just in case), the Hachiman Bell, Solar Gem, Tengu Sandals and Guiding Doll.
Run through his Osaka Infiltration a few times to get the feel of the map. Try and find the shortest route to the stairs and memorize treasure locations.
The Caper
Begin Goemon's Osaka Infiltration on Hard difficulty.
Save your energy. Do not attempt to engage any enemies. This will only waste time. Time is very much against you on this one.
Collect enough treasure to move to the second floor, then do so.
Search all the rooms on the second floor. You will get a message from Goemon (apparently he likes to talk to himself) when there are 3 rooms left, then again when there is 1 left. If you can pull this off in under 5 minutes, you will get the special item report. The box will appear in front of the stairs to the third floor.
Finish the stage and enjoy your new cannon and club!